British, French, Italian, and German jets have simulated flight interceptions over Western Europe as part of NATO maneuvers to deter Russian planes from entering alliance airspace.

The NATO drills on September 12 came at the same time that Russia was showing off its most sophisticated air-defense system as it practiced fighting off a mock attack during military maneuvers of its own, the largest it has ever conducted.

The activity comes amid persistently high tensions between Russia and the West over Moscow's actions in Ukraine and Syria and its alleged interference in elections in the United States and European countries.

In the NATO drills, fighter pilots from alliance members simulated the interception of a Belgian military transport plane en route to Spain. Visual inspections were made by flying off the wings at speeds of 900 kilometers an hour.

NATO has some 60 jets regularly on alert to defend its airspace. A record 870 interceptions were recorded of Russian aircraft in the Baltic region in 2016.

"NATO is relevant. This is not theoretical," Spanish Air Force Lieutenant General Ruben Garcia Servert said aboard the Belgian plane.

As he spoke, Italian Eurofighters flew close to the cockpit to simulate interceptions, later joined by British Typhoons and French Mirages.

The European members of NATO are looking to display their commitments to their defense in the face of criticism by U.S. President Donald Trump that alliance members are not contributing enough financially to the alliance.

The Western alliance is currently negotiating an agreement that would have each member's air force defend any other's airspace under a "single sky" concept.

Currently, each country defends its own airspace, although other members help defend the airspace of the Baltic states, which do not have enough fighter jets of their own.

NATO is planning to hold its biggest maneuvers in 16 years when it conducts the Trident Juncture drills in Norway in October and November.

The drills will feature more than 40,000 troops, including some from non-NATO members Finland and Sweden.

Meanwhile, Russia is conducting massive military exercises across its central and eastern regions, weeklong war games the Defense Ministry said would involve some 300,000 personnel -- twice as many as the biggest Soviet maneuvers of the Cold War era.

On September 12, the war games involved Russia's newest S-400 surface-to-air defense system, which NATO considers a threat to its aircraft.

Moscow last year signed a contract to sell the S-400 system to Turkey, angering NATO and particularly the United States, which threatened to suspend delivery of its F-35 stealth aircraft to Ankara.

The drills simulated a "massive missile attack" by an "unnamed enemy," military official Sergei Tikhonov said.

The exercises, which also involve Chinese and Mongolian soldiers, will run through September 17.